Compressors used in refrigeration, air conditioning and heat pump systems are normally mounted to the associated base pan through a vibration isolating mounting assembly. Specifically, compressors are commonly mounted to the base pan of the condensing or outdoor unit. In such an installation, it is desirable to damp vibrations and the resultant noise caused by operation of the compressor. A common arrangement is to locate elastomeric grommets between the base or feet of the compressor and the base pan upon which it is mounted. The grommets have lips and necks which permit their insertion into openings in the base or feet of the compressor which generally correspond to the neck dimensions. The compressor, with attached grommets, is set on the base pan which has a plurality of threaded studs secured thereto. The threaded studs are then pushed through the grommets as the compressor is set on the base pan. Nuts are threaded to the studs to secure the connection.
The grommets support the weight of the compressor and are radially spaced from the center of gravity of the compressor to prevent it from tipping. While the spaced supports provide stability, they also increase the torsional restoring forces due to their distance from the axis of rotation. The grommets serve to vibrationally and acoustically isolate the compressor from its support. The resonance frequencies of the compressor torsional and rocking modes are inherently high in such a mounting arrangement, tending to fall into the proximity of the compressor speed and to cause vibration and noise problems. To alleviate these problems, the grommets are normally made very soft in the transverse directions which may result in excessive movement during shipping causing damage to the piping and/or coils in the system. Because movement of the compressor base or feet is a shearing or cutting movement relative to the necks of the grommets, their weakest point, damage may occur to the grommets. Besides being vulnerable to damage, installation is difficult due to the grommet lips, and the neck represents a small clearance between the compressor foot and the studs such that a short circuit for vibration can be created upon the cutting of the neck.
In addition to vibrationally and acoustically isolating the compressor from its support during operation, they also cushion the compressor during shipping. Tipping, dropping and the like can subject the compressor to forces and magnitudes of forces not encountered in normal operation. Upon severe tipping, or the like, the lip, or a portion thereof, may be pulled through the compressor base or foot such that the isolator will be subsequently damaged and/or ineffective.
The grommets of the compressor mounting assembly are preferably made without necks but, if present, can be made larger and with a clearance around the necks since the grommets are received and engaged, at the location of their greatest radial extent, in annular recesses in the compressor feet or base. With the elimination of the lips or heads due to the elimination of the necks, rubber washers, or the like, may be optionally located between the compressor feet or base and the nuts on the studs holding the assembly in place during shipping. If rubber washers, or the like, are not used, the spacing between the compressor feet and the nuts must be less than the depth of the annular recesses such that the grommets will not be withdrawn from the recesses as when tipping occurs.
It is an object of this invention to facilitate grommet installation.
It is another object of this invention to reduce isolator failure due to cutting of the grommets.
It is a further object of this invention to reduce forces transmitted to the base pan from a compressor.
It is another object of this invention to attenuate compressor generated sound.
It is a further object of this invention to provide improved vibration isolation of a compressor. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, the base pan of a refrigeration, air conditioning or heat pump system is overlain by a series of assemblies each serially including a grommet, a compressor foot or base and, optionally, a washer or the like. The compressor foot or base defines a plurality of recesses for receiving one end of each grommet and are of such a depth as to retain the grommets when the compressor is subject to tipping or the like. A stud or bolt extending through each assembly, and coacting with a nut, secures the respective assembly to the base pan.